Travelling wave tube with positive ion drainage



D. REVERDIN Oct. 19, 1965 TRAVELLING WAVE TUBE WITH POSITIVE ION DRAINAGE Filed April 26, 1960 2 Sheets-Sheet l INVENTOR.

DANIEL REVERDIN n x I! ATTORNEY D. REVERDIN Oct. 19, 1965 TRAVELLING WAVE TUBE WITH POSITIVE ION DRAINAGE Filed April 26, 1960 2 Sheets-Sheet 2 INVENTOR.

DANIE L REVERDIN United States Patent TRAVELLING WAVE TUBE WITH PQSITIVE HUN DRAINAGE Daniel Reverdin, Paris, France, assignor to Compagnie Generale de Telegraphie Sans Fil, Paris, France Filed Apr. 26, 1960, Ser. No. 24,825

Claims priority, application France, May 26, 1959,

795,590 18 Claims. (Cl. 315-) The present invention relates to travelling wave tubes of rectilinear structure of which the beam or beams are focused by a longitudinal magnetic field and propagate in an equipotential space, such tubes being commonly known in the prior art as O-type tubes.

One disadvantage known in the prior art in connection with these tubes resides in the fact that the vacuum is never perfect so that the electron beam or beams ionize the residual atoms of the gaseous medium present within the tube, whereby the residual atoms, once they become positive charges, are moving toward the regions of the most negative potential, and particularly toward the beam. As the positive charges become intermingled with the electrons of the beam or beams, they form a plasma which is imprisoned or enclosed within the depressions formed in the beam by reason of the successive thickening and thinning imposed thereupon by the magnetic focusing field. This plasma is therefore carried by the beam. It is known that unde these conditions the plasma begins to oscillate at frequencies located between some kilocycles per second and some megacycles per second which introduces a frequency modulation in the frequency of operation of the tube, and an amplitude modulation in the output power of the tube, phenomena which are particularly annoying if the tube is to operate as auto-oscillator.

It has already been proposed in the prior art to remedy this inconvenience by disposing parallelly to the delay line a conducto carried at a potential slightly different from that of the delay line, whereby the electric field between the conductor and the delay line serve to drain the ions which are moving either against the line or against the conductor depending upon the direction of the field, the US. Patent 2,610,308 to Touraton being representative of the prior art attempts to alleviate the inadequacies of the prior art O-type tubes.

It has also been found that such arrangement is particularly effective when the potential of the conductor is negative, that is when the ions are drained toward the conductor, and that the efficacy is the better the greater the absolute value of this potential. There exists, therefore, a direct interest to utilize a negative potential which is as high as possible. However, any attempts to improve the efiicacy of the tube in this. direction are quickly limited, for the difference in potential between this conductor and the elements of the tube carried at the potential of the equipotential interaction space ends up by creating within this space an electric field that is sufficiently strong to have some influence on the electron trajectories or paths which in turn would disturb the proper operation of the tube which thereupon ceases in fact to be an O-type tube.

The object of the present invention is an O-type tube, provided with one of several negatively biased draining conductors for the drainage of ions in which the shortcomings encountered in the prior art and mentioned hereinabove are eifectively eliminated in such a manner that it is possible to apply to such conductor or conductors a negative potential which is relatively elevated without, however, incurring that the tube ceases to operate as an O-type tube.

3,213,314 Patented Got. 19, 1965 Accordingly, it is an object of the present invention to provide a travelling wave tube normally operating as an O-type tube which eliminates the inadequacies and shortcomings of the prior art devices and which eifectively prevents the formation of any plasma within the tube caused by residual gaseous atoms.

Another object of the present invention is the provision of a travelling wave tube in which the deleterious effects of gaseous residual atoms are effectively eliminated by the removal or drainage of charged particles resulting therefrom without impairing the operation of the tube for its intended purposes.

Still another object of the present invention resides in the provision of an O-type travelling wave tube in which spurious oscillations due to residual gaseous atoms combining with electrons of the beam or beams into a plasma is effectively prevented.

Still another object of the present invention resides in the provision of means for effectively eliminating from the tube charged particles resulting from residual gas atoms to prevent any interaction thereof with the electron movement, without, however, impairing the electron fiow.

These and other objects, features and advantages will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, several embodiment in accordance with the present invention and wherein FIGURE 1 is a longitudinal cross-sectional view of a first embodiment of a travelling wave tube in accordance with the present invention, of the type commonly known as O-type Carcinotron oscillator,

FIGURE 2 is a transverse cross-sectional view taken along line 22 of FIGURE 1,

FIGURE 3 is a partial cross-sectional view taken along line 33 of FIGURE 2, with a plan view of the electrode system at the inside of the envelope,

FIGURE 4 is a longitudinal horizontal cross-sectional view through the electrode system of FIGURE 3 taken in a plane perpendicular to the drawing of FIGURE 3,

FIGURES 5 and 6 are cross-sectional views, similar to FIGURE 2, of two modified embodiments in accordance with the present invention,

FIGURES 7 and 8 are cross-sectional views, similar to FIGURE 3, of two further modified embodiments in accordance with the present invention, and

FIGURE 9 is a longitudinal cross-sectional view corresponding to the transverse cross-sectional view of FIG- URE 6.

The invention essentially consists in utilizing such conductor or conductors in combination with a delay line of the back-plat type, by disposing the drainage conductor or conductors relatively in proximity to this backplate, in such a manner that the electric field created about these conductors by the application of the negative potential is strongly heterogeneous so that the largest majority of lines of force extend toward the back-plate whereas the interaction space is traversed only by a relatively small number of lines of force in such a manner that the electric field prevailing within the interaction space is insufiicient to disturb, in a perceptible manner, the movement of the electrons.

It may be remembered that the back-plate utilized with conventional delay lines is a conductive surface spaced from the delay line, whereby this conductive surface may be either cylindrical and surround the delay line or may be plane and be connected to the delay line by lateral walls in the case of a delay line of plane configuration, the assembly thereby forming a box-like configuration of which the interior space is equipotential.

According to one preferred embodiment of the present invention, the drainage conductor or conductors are disposed in one or several slots provided in the back-plate or in the lateral walls of the box in the case of a plane delay line.

Accordnig to a modified embodiment of the present invention, the conductor or conductors may be disposed directly below the back-plate.

These conductors may thereby extend in any suitable, appropriate direction, for example, in the longitudinal or transverse direction. In the case of a longitudinal orientation, the conductors may extend either over the entire length of the delay line or only over a portion thereof, for example, adjacent the collector end thereof.

Refering now to the drawing wherein like reference numerals are used throughout the various views to designate the corresponding parts, and more particularly to FIGURES l to 3, reference numeral 1 designates therein a cylindrical envelope or enclosure, for example, made of glass and soldered or secured in any other suitable manner to a solid matallic collector 2. An electron gun including a filament 3, a cathode 4 and an accelerating anode 5 provided, for example, with two slots 6 for the passage therethrough of two electron beams 7 in the form of ribbons is provided within the envelop 1. The beams 7 pass on both sides of the interdigital delay line 8 of which a certain number of fingers on the side of the collector 2 are covered with an attenuation means 9 of conventional construction illustrated schematically in the drawing by cross-hatching. The delay line 8 is brazed to a pair of back-plates 10 which surround the same on both sides and form a box therewith.

According to the present invention, the back-plates 10 are provided with longitudinal slots 11 within the surfaces thereof parallel to the delay line in which slots are disposed longitudinal bars 12, insulated from the delay line and forming draining conductors. The bars 12 are suspended by means of screws on insulating laminates or strips 13 which in turn are secured to the walls of the back-plates 10 by means of screws 19.

The filament 3 is heated by a suitable source 15 and the cathode 4 is connected to the potential thereof. A potential positive with respect to the cathode 4 is applied by means of a suitable source 16 to the accelerating anode 5, to the collector 2 and to the assembly of the delay line 8 with back-plates 10 which are electrically connected to the collector 2. Finally, a negative potential with respect to the delay line 8 is applied to the bars 12 by means of a suitable source 17, and of connections 18 passing through the end or base part of the envelope 1 and connected to the screws 14. The optimum value for this potential may be determined experimentally from the compromise between the disappearance of the annoying phenomena and the condition of non-disturbance in the operation of the tube by the resulting electric field. If such experimental determination leads to the same value of potential for the source 17 as for source 16, then the source 17 may be eliminated and the connection 18 may be connected directly to the cathode 4.

A coaxial output coupling 20 (FIGURES 2, 3 and 4) is accommodated or secured laterally to the delay line 8. The outer conductor of the coaxial output coupling 20 is threadably connected within the collector 2 whereas 'the inner conductor 21 thereof is directly secured to the first finger 22 of the delay line 8 adjacent the end thereof near the electron gun which finger 22 is elongated for that purpose and enters into the coaxial coupling through the orifice 23. The inner conductor 21 passes through the collector 2 and terminates in an output lead 24.

A magnetic winding 25 which may also be replaced by a suitable permanent magnet, provides the'necessary magnetic field required for purposes of focusing the beams 7.

The operation of the tube disclosed herein does not require a detailed description since the mechanism of oscillations of the Carcinotron type oscillators s well-known in the art and since the drainage effect on the ions by conductors analogous to the bars 12 of the present invention is also known. Nevertheless it should be noted that the tube described herein provides unexpected and unforeseeable improved results, characterized by the complete disappearance of parasitic modulation of the oscillation produced, and without the accompanying appearance of other disturbances in the operation of the tube as was the case inherently in the prior art devices. This improvement may be attributed to the arrangement of the bars 12 in the slots 11 of the back-plates 10, a disposition thereof thanks to which the electric field about the bar 12 becomes strongly heterogeneous in such a manner that the majority of the lines of force extend toward the re spective back-plate 10 whereas the number of lines of force extending toward the delay line 8 is relatively small in such a manner that the space at the interior of the box of the delay line assembly does not cease, for all practical purposes, to be equipotential even if the bar 12 is carried at the potential of cathode 4.

FIGURE 5 illustrates a cross-sectional view, analogous to that of FIGURE 2, of a modification in accordance with the present invention in which the bars 12 are located in slots provided in the lateral walls of the backplate 10. The bars 12 are secured therein between two insulating strips 26.

FIGURE 6 also illustrates a cross-sectional view, analogous to that of FIGURE 2, of still another modified embodiment according to the present invention in which there are no slots at all in the back-plate 10 which is, for example, of cylindrical form in this case, and in which the drainage conductor is constituted by a wire 27 suspended directly below the back-plate 10, for example, in the longitudinal direction of the tube.

However, this longitudinal direction is not indispensable, and FIGURE 7 represents a cross-sectional view, analogous to that of FIGURE 3, of a modified embodiment in which the longitudinal slots 11 in the back-plate 10 of FIGURE 3 are replaced, for example, by two transverse slots 28 in which are located the bars 29 equivalent to the bars 12 and suspended and supplied with a suitable voltage in the same manner as the latter. The operation of this system is analogous to that of any of the preceding figures.

The same transverse arrangement however, may also be used obviously in connection with the wires 27 of FIGURE 6.

It is not necessary, however, that the drainage conductors extend along the entire delay line, quite to the contrary there may be provided in conformity with FIG- URE 8 which shows a cross-sectional view analogous to that of FIGURE 3, an embodiment in which the bar 12 extends only over a portion of the circuit, for example, over the attenuated zone of the collector end thereof in the case of a Carcinotron oscillator. The slot 11 is thereby shortened correspondingly. Consequently, this arrangernent completely frees the device of any influence of the field produced by the drainage electrode on the beam essentially over the entire useful extent thereof.

The same shortened arrangement could obviously be applied also to the wires 27 in FIGURE 6'. By limiting the length of these Wires 27 to approximately one-third of the length of the delay line 8 and by placing the same near the collector end of the tube, it is possible to electrically connect the wires to a very high negative potential, for example, the same potential as the cathode 4 without disturbing the characteristics of the tube.

Such an arrangement is illustrated in FIGURE 9 which shows a longitudinal cross-sectional View through a backplate 10 provided with a wire 27 suspended over a portion A-B of the back-plate corresponding to approximately one-third length of the delay line, and traversing the back-plate 10 across two insulating passages 30 and 3t). The extremity C is thereby left free Whereas the extremity D thereof is connected to the cathode 4.

It has been noted experimentally that in all of the cases indicated hereinabove the drainage of ions and of secondary electrons produced by the impact of ions on the drainage conductor is completely satisfactory and that any parasitic modulation completely disappears.

While I have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of many changes and modifications within the spirit and scope of the present invention. For example, the present invention is not limited to tubes utilizing a plane delay line as illustrated. Quite to the contrary, the present invention may be applied equally elfectively according to the same principles in combination with delay lines having a back-plate of cylindrical symmetry. Additionally, the present invention is not limited in its application to Carcinotron type or backward-wave-type oscillators but may be used with any other type of O-type amplifier or oscillator tube with feedback.

Thus, it is quite obvious that the present invention is sucesptible of many changes and modifications within the spirit and scope thereof, and I, therefore, do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. A travelling wave tube having a delay line provided with at least one back plate, means in said tube for producing at least one electron beam adapted to propagate within a space adjacent said delay line, focussing means for said beam including magnetic field generating means with the lines of force thereof directed essentially longitudinally along said beam, at least one electrical conductor fixed substantially parallel to said delay line, and potential means for applying to said conductor a negative potential with respect to said delay line to drain ions formed within said space, said conductor being located substantially closer to said back plate than to said delay line.

2. A tube as claimed in claim 1, wherein at least one slot is provided within said back plate, and wherein said conductor is located within said slot.

3. A tube as claimed in claim 1, wherein at least a predetermined length of said conductor is located in said space adjacent said back plate.

4. A tube as claimed in claim 1, wherein said conductor extends longitudinally with respect to said beam.

5. A tube as claimed in claim 1, wherein said conductor extends transversally with respect to said beam.

6. A tube as claimed in claim 1, wherein said first-mentioned means includes a cathode, and wherein said conductor is effectively connected to the potential of said cathode.

7. A tube as claim in claim 1, further comprising a collector for collecting said beam, and wherein said conductor extends over a portion of said delay line on the side neighbouring said collector.

8. A tube as claimed in claim 7, wherein said portion has a length of about one third of said delay line length.

9. A travelling wave tube comprising delay line means delimiting at least in part an interaction space, means for injecting at least one beam of electrons into said interaction space including focussing means, and auxiliary means including at least two conductive members disposed contiguous to but outside said interaction space with one of said members carried at a negative potential with respect to the other conductive member and with respect to said delay line means in such a manner as to produce an electric field of which only relatively few lines of force extend into said interaction space.

10. A travelling wave tube comprising a wave guiding structure including a first non-periodic portion and a second periodic portion for propagating therealong electromagnetic wave energy, said tube being provided with an interaction spaced formed at least in part by the second periodic portion of said wave guiding structure, means adapted to produce an electron flow within said interaction space adapted to interact with a space harmonic propagating along said wave guiding structure, and auxiliary electrode means adapted to be carried at a negative potential with respect to said wave guiding structure for effectively draining residual ions from said tube by the electric field produced between said auxiliary electrode means and said wave guiding structure, said auxiliary electrode means being so constructed and arranged that said electric field has a majority of the lines of force thereof avoid said interaction space.

11. A travelling wave tube according to claim 10, wherein said tube is an O-type tube having an essentially equipotential interaction space.

12. In a microwave apparatus, delay line means for propagating electromagnetic wave energy and defining at least in part an equipotential interaction space, conductive means located essentially outside said interaction space and associated with said delay line means, means for producing at least one electron stream in said interaction space past said delay line means at a velocity for interaction with said wave energy, and auxiliary means carried at a potential with respect to said conductive means for producing an electric field between said auxiliary means and said conductive means leaving said equipotential field essentially unaffected for draining ions from said tube to prevent the formation of a plasma by the combination of said ions with electrons of said electron flow.

13. The combination according to claim 12, wherein said second-mentioned means includes magnetic focus ing means having lines of force extending approximately parallelly to said electron stream.

14. The combination according to claim 12, wherein said microwave apparatus is a backward wave amplifier.

15. The combination according to claim 12, wherein said microwave apparatus is a backward wave oscillator.

16. The combination according to claim 12, wherein said microwave apparatus is a forward wave amplifier.

17. The combination according to claim 12, wherein said microwave apparatus is a forward wave oscillator having feed back means.

18. In an electron discharge device comprising an electron source, a wave guiding structure having a first portion etfectively constituting a delay line for propagating therealong electromagnetic energy and a second conductive portion essentially devoid of any delay characteristics, an equipotential interaction space limited at least in part by the first portion of said wave guiding structure, means for directing the electrons from said source into said interaction space at such velocity as to enable interaction thereof with a space harmonic of said energy including focussing means, and auxiliary means carried at a negative potential with respect to the second portion of said wave guiding structure and located in such a manner with respect thereto as to produce a heterogeneous electric field with the majority of the lines of force bypassing said interaction space.

References Cited by the Examiner UNITED STATES PATENTS 2,610,308 9/52 Touraton et al. 3l5-3.5 2,707,759 5/55 Pierce 3l5-3.6 2,767,344 10/56 Hines 315--3.5 2,794,936 6/57 Huber 3l5-3.6 2,890,374 6/59 Charles et al. 3153.6 2,976,454 3/61 Birdsall et al. 3l53.5

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSEN, Examiner. 

1. A TRAVELLING WAVE TUBE HAVING A DELAY LINE PROVIDED WITH AT LEAST ONE BACK PLATE, MEANS IN SAID TUBE FOR PRODUCING AT LEAST ONE ELECTRON BEAM ADAPTED TO PROPAGATE WITHIN A SPACE ADJACENT SAID DELAY LINE, FOCUSSING MEANS FOR SAID BEAM INCLUDING MAGNETIC FIELD GENERATING MEANS WITH THE LINES OF FORCE THEREOF DIRECTED ESSENTIALLY LONGITUDINALLY ALONG SAID BEAM, AT LEAST ONE ELECTRICAL CONDUCTOR FIXED SUBSTANTIALLY PARALLEL TO SAID DELAY LINE, AND POTENTIAL MEANS FOR APPLYING TO SAID CONDUCTOR A NEGATIVE POTENTIAL WITH RESPECT TO SAID DELAY LINE TO DRAIN IONS FORMED WITHIN SAID SPACE, SAID CONDUCTOR BEING LOCATED SUBSTANTIALLY CLOSER TO SAID BACK PLATE THAN TO SAID DELAY LINE. 